Sweetpotatoes (Ipomoea batatas) are a perennial herbaceous dicotyledonous species of the morning glory family Convolvulaceae. Sweetpotatoes, unlike the Irish potatoes (Solanum tuberosum), are not a tuber propagated plants. A “tuber” is a short, thickened portion of an underground branch. Along a tuber are found “eyes,” each of which comprises a ridge bearing a scale-like leaf (analogous to a branch leaf) having minute meristematic buds in the axial of the leaf. By contrast, sweetpotato roots are developmentally and anatomically true roots, lacking meristematic buds, and are not derived from an underground branch. Sweetpotatoes do not form tubers.
Sweetpotato plants produce primary fibrous roots, pencil roots and storage roots. Storage roots are attached to the stem by a stalk of thinner root that is usually initiated at the stem node just below the soil line. Skin color of storage roots typically ranges from white to brown to red-orange. Flesh color of storage roots is typically red-orange, orange, yellow or white. The flesh can be either soft or firm.
A few sweetpotato varieties produce storage roots with purple flesh, or purple skin, or both purple flesh and purple skin. These varieties may be desirable for any combination of their salability, unique flavor or nutritional benefit. These varieties produce various anthocyanins, which cause the purple color. Anthocyanins have attracted attention because they have multiple physiological properties, including radical-scavenging (or antioxidative), anti-mutagenic, hepato-protective, antihypertensive, and antihyperglycemic properties. Because of these beneficial properties, the more anthocyanins, or the greater the variety of anthocyanins, that can be produced in the storage root, the better.
One way to gauge the extent or the variety of anthocyanins is to look for stability of the purple color after heat stress, e.g. cooking. The degree of color stability after heating is correlated with the number of anthocyanin species.
It is thus desirable to produce a larger variety of sweetpotato with purple flesh and purple skin. It is further desirable to produce a variety of sweetpotato with purple flesh and purple skin that has the ability to grow in the southeastern United States. It is further desirable to produce a sweetpotato with purple flesh, which maintains its purple color after heat stress.